Process for preparing particulate products having preferentially internally concentrated core components

ABSTRACT

GRANULAR PARTICLES COMPRISING A PARTIALLY HYDRATED INORGANIC SALT AND A CORE COMPONENT, THE CORE COMPONENT BEING PREFERENTIALLY INTERNALLY CONCENTRATED IN THE PARTICLES, ARE PREPARED BY SPRAYING AN AQUEOUS MEDIUM CONTAINING THE CORE COMPONENT ONTO A FLUIDIZED BED OF HYDRATEABLE INORGANIC SALT. SUCH PARTICLES WHEREIN THE CORE COMPONENET IS, FOR EXAMPLE, A CHLOROCYANURATE ARE USEFUL INGREDIENTS OF DETERGENT COMPOSITIONS WHEREIN THEY EXHIBIT EXCELLENT CHEMICAL AND PHYSICAL STABILITY.

PROCESS FOR R. B. HUDSON 3,650,961 PREPARING PARTICULATE PRODUCTS HAVINGPRBF'ERENTIALLY INTERNALLY CONCENTRATED CORE COMPONENTS Filed July 18,1969 )f/fi/ ////x// 1 atent Patented Mar. 21, 1972 PROCESS FOR PREPARINGPARTICULATE PROD- UCTS HAVING PREFERENTIALLY INTERNALLY CONCENTRATEDCORE COMPONENTS Robert B. Hudson, St. Louis, Mo., assignor to MonsantoCompany, St. Louis, Mo. Filed July 18, 1969, Ser. No. 842,890 Int. Cl.344d 1/095; Clld 7/42, 7/56 U.S. Cl. 252--99 6 Claims ABSTRACT OF THEDISCLOSURE Granular particles comprising a partially hydrated inorganicsalt and a core component, the core component being preferentiallyinternally concentrated in the particles, are prepared by spraying anaqueous medium containing the core component onto a fluidized bed ofhydrateable inorganic salt. Such particles wherein the core componentis, for example, a chlorocyanurate are useful ingredients of detergentcompositions wherein they exhibit excellent chemical and physicalstability.

BACKGROUND OF THE INVENTION This invention relates to a novel, fluidizedbed process for making granular compositions composed of particlesocmprising a core component preferentially internally concentrated orsubstantially encapsulated within a matrix or coating of partiallyhydrated inorganic salt. The invention further relates to novelcompositions of the aforesaid type wherein the partially hydratedinorganic salt comprises a major proportion of phosphate salts, at least90% by weight of the phosphate salts being sodium tripolyphoshate.

It is well-known that the practical utility of numerous materials islimited by physical or chemical incompatibility with ingredients offormulations in which they would otherwise be desirably employed, or,with atmospheric moisture under normal storage conditions. Problems ofthis type are encountered, for example, with many chlorocyanurate drybleaching compounds. Commercially available chlorocyanurates aregenerally in the form of very fine particles which, when mixed withvarious carrier agents, tend to segregate or stratify therefrom. SuchStratification is undesirable since it renders the packaged compositionnon-homogeneous and uniform results are not obtained as successiveportions of the package are utilized. Thus, the chlorocyanurate isconsidered physically incompatible in such mixtures. In addition, thechlorocyanurates tend to decompose in contact with atmospheric moisturethereby loosing chlorine available for bleaching and producing anundesirable chlorine odor. The chlorocyanurates also tend to be reactivewith certain conventional detergent ingredients, for example, nonionicsurfactants, and cannot be readily combined with such ingredients toprovide stable, all-purpose bleaching-cleaning formulations. Thoseskilled in the art, will, of course, recognize numerous problems of thistype inherent in a variety of materials used not only in detergent andbleaching formulations but in numerous other applications.

It is further recognized by those skilled in the art that problems ofthe type discussed above associated with various materials can beeliminated or greatly reduced by providing the physically or chemicallyincompatible material With a protective coating. Coating orencapsulation of particulate materials can be conveniently accomplishedby fluidized bed techniques. In techniques of this type, the particulatematerial to be coated is formed into a fluidized bed in accordance withwell-understood engineering principles (see, for example, Fluidizationby Max Leva,

McGraw-Hill, 1956) and a slurry or solution of the coating material issprayed onto the fluidized particles. The particles, coated with thesolution or slurry, are then subjected to a drying operation to removefree water or other solvent and, in some instances, water of hydration.Processes of this type as applied to coating of chlorocyanurates aredescribed, for example, in U.S. Pat. No 3,112,274.

Although such processes are effective to coat a variety of materials,the necessity of providing a drying step to remove water associated withthe coating material is undesirable. Obviously, such drying steps areexpensive and time consuming. More importantly, the temperature requiredfor drying, particularly if removal of water of hydration is required,often results in degradation of the coating or of the encapsulatedmaterial. For example, dehydration of sodium tripolyphosphatehexahydrate results in extensive hydrolytic degradation to ortho andpyrophosphates.

SUMMARY OF THE INVENTION It is an object of this invention to providenovel fluidized bed processes for making compositions composed ofparticles comprising a core component preferentially internallyconcentrated within a partially hydrated inorganic salt matrix orcoating. A further object is to provide such processes wherein thepartially hydrated form of the salt is obtained without necessity of aseparate drying step. Still another object is to provide a compositionof the type referred to above wherein the partially hydrated inorganicsalt comprises a major proportion of phosphate salts at least by weightof such salts being sodium tripolyphosphate.

These objects are achieved by introducing droplets of an aqueous slurryof core component material into a fluidized bed of hydrateable,particulate, inorganic salt. The size of the slurry droplets and saltparticles and the fluidization conditions are controlled as hereinafterdescribed.

The invention will be more clearly understood from the drawings and thefollowing description of the preferred embodiments.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of apparatussuitable for practicing this invention and illustrating the flow ofmaterials therein.

FIG. 2 is a sectional illustration of another embodiment of apparatussuitable for use in the practice of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The basic operationalprinciples of the process of this invention will be understood byreference to the drawings.

Referring to FIG. 1, particulate, hydrateable inorganic salt 10, isintroduced through inlet tube 12 into a chamber defined by walls 14. Theparticulate salt is fluidized by a flow of inert gas through porousplate 16. Droplets 18, of an aqueous slurry of core component materialare sprayed onto the fluidized bed of inorganic salt from spray head 20.The fluidized salt coats the droplets, absorbing water therefrom andforming a particle wherein the core component is preferentiallyconcentrated internally in the particle comprising the core componentand partially hydrated inorganic salt. Referring again to FIG. 2, theparticles formed being of greater mass than the hydrateable inorganicsalt, fall in the fluidized bed and are removed through exit tube 22.

The process can also be performed in batch type apparatus, That is,although continuous introduction of ingredients into the fluidized bedand simultaneous removal of products are generally desirable, suchcontinuous operation is not essential to the practice of this invention.

If desired, fluidization of the inorganic salt can be accomplished bymechanical rather than pneumatic means. For example, as shown in FIG. 2,a bed of inorganic salt 10 can be fluidized by rapid rotation ofimpeller blade 26. However, since mechanical fluidization may result insome degree of comminution of product particles, pneumatic fluidizationwith an inert gas is generally preferred. The term inert gas is used ina broad sence to include any gas which is substantially non-reactivewith the inorganic salt particles and the core component material. Thus,air as well as helium, argon, nitrogen, and the like generallyconstitutes an acceptable fluidizing gas.

It is recognized by those skilled in the art that when an aqueous mediumis sprayed onto a bed of fluidized particles that the particles withinthe bed are normally coated with the aqueous medium. Therefore, it isextremely surprising that a process of the type described results inmaterials introduced in aqueous medium being coated by or preferentiallyinternally concentrated within a matrix of the fluidized particles. Toobtain this unique result, control of chemical and physicalcharacteristics of the particles constituting the fluidized bed, thedegree of fluidization of such particles, and the manner of introducingthe core component material is required.

The particles used to form the fluidized bed must, of course, bechemically compatible with the core component material so as to avoidformation of substantial quantities of undesired reaction products. Itwill be understood that complete inertness is not required and somereactivity may be desirable if the reaction product thus obtained is notdetrimental. The selection of materials based on chemical reactivity orinertness will be readily apparent from general principles governingchemical reactivity or from routine tests.

The material used to form the fluidized bed of this invention must be areadily hydrateable inorganic salt. That is, the inorganic salt must becapable of taking up the water from the droplets as water of hydration.Otherwise, a separate drying step is required. Generally, the use ofsubstantially anhydrous salt is preferred although partially hydratedsalt may be employed if desired. The term partially hydrated salt refersto lower hydrates of salts capable of forming higher hydrates, ormixtures of anhydrous and fully hydrated particles. Examples of saltssuitable for use as an encapsulating material include: N35P3010N214P2O']; Na SO Na2B407; CuSO Na3PO4; Na CO Na HPO partial hydratesthereof, and mixtures thereof. The polyphosphate salts, especiallysodium tripolyphosphate are particularly preferred when the product isto be used in detergent, water-softening, or bleaching compositionssince such salts are known to be functional components in suchcompositions.

The hydrateable inorganic salts used in the fluidized bed must consistof particles, a major proportion of which have a size of from 5 to 200microns, preferably from to 150 microns, a size of 10 to 50 micronsbeing particularly preferred. Particle size is determined by gravimetricsedimentation type analysis. Smaller sized particles are swept from thebed under normal fluidization conditions and larger fluid bed particlesdo not form product particles wherein the core component ispreferentially internally concentrated. Relative uniformity of fluid bedparticle size is desirable but not essential.

Any slurry forming material meeting the chemical compatibilityrequirements discussed above can be utilized as the core component. Forexample, enzymes such as produced by Bacillus, Aspergillus, orStreptomyces micro-organisms including B. subtilis strains NRRL B-3411and NRRL B-34l1 (U.S. Department of Agriculture Collection) and IAM 1523(Japanese Culture Collection) all of which produce mixtures of proteasesand amylases, and B. lichenformis which produces a predominantlyalkaline protease; and chlorocyanurates, such as sodium and potassiumsalts of diand tri-chloro cyanuric acid, [(monotrichloro,)tetra-(mono-potassium dichloro,)] pentaisocyanurate, and (trichloro,)(monopotassium dichloro,) di-isocyanurate can be effectively internallyconcentrated within a matrix of or coated with partially hydratedpolyphosphates to form stable detergent ingredients.

The core component material is dispersed as a slurry in water anddroplets of the slurry are introduced into the fluidized bed. If thecore component is a highly water soluble material, for example, certainwell-known enzymes, the slurry is formed by salting out the corecomponent, for example, by adding isopropanol or more preferably, analkali metal salt such as sodium or calcium sulfate. The degree ofpreferential concentration of the core component in the interior of theparticles of this invention is related to the solubility andconcentration of the core component in the slurry. The degree ofpreferential concentration may be such that the product particlecomprises a center of core component encapsulated within partiallyhydrated Salt, or core component may be distributed through a saltmatrix in gradually decreas ing concentration from center to peripheryof the particles. Addition of a slurry of relatively insoluble corecomponent to the bed results in a product particle wherein the corecomponent is essentially encapsulated within an inorganic salt shellrelatively free of core component material. Such preferential internalconcentration of this core component decreases as the core componentbecomes more soluble.

The quantity of slurry introduced into the fluidized bed is controlledso that the water present therein is less than that stoichiometricallyrequired for total hydration of the hydrateable inorganic salt, and isgenerally from 20 to 70% by weight of the stoichiometric quantity. Thus,in the product particle, the salt is only partially hydrated. Theincompletely hydrated salt is capable of protecting the core componentby taking up additional water from the atmosphere. Attempts to obtaincomplete hydration is not only undesirable from a standpoint of optimumstability, but also usually causes caking in the fluid bed andagglomeration of discrete composite particles which have already formed.

The mean diameter of droplets of the slurry of core component materialmust be from about 10 to 30 times larger than the mean particle size ofthe particles comprising the fluidized bed to provide preferentialinternal concentrations of the core component in product particles. Thedroplet size is readily controlled by proper choice of spray head,nozzle, or other means for introducing the droplets into the fluidizedbed.

In the practice of this invention, the fluidization of the bed ofhydrateable inorganic salt should be such that the fluidized saltoccupies a volume of at least 1.2 times greater than an identicalquantity of unfluidized salt. That is to say, a quantity of hydrateableinorganic salt having a static volume of cubic centimeters will, whenproperly fluidized in accordance with this invention, occupy a volume ofat least cubic centimeters. A fluidization volume of about 1.4 to 2.0times the static volume is preferred. For many applications, it isdesirable to use a so-called spouted bed in which there is a distributedflow of gas suflicient to cause fluidization and one or more 10- calizedheavier flows of gas which cause the bed to spout upward and tocirculate rapidly. The spouts may be in the form of single jets or inthe form of a ring of jets near the wall of the containing vessel. Suchspouts of rapidly rising gas and material have suflicient velocity to-throw the bed material well above the upper bed level established bythe distributed gas flow. A spouted bed is particularly useful inconjunction with core components materials that retard the hydration ofthe hydrateable salt.

In pneumatically fluidized beds, particularly spouted beds whereinmeasurement of bed volume is diflicult, the

proper degree of fiuidization can be more conveniently express =as afluidizing gas flow rate from to 100% in excess of the minimumtheoretically required to sustain a fluid bed, as measured by pressuredrop through the bed.

It is possible to practice this invention by spraying the core componentmaterial into a flow of hydrateable salt particles entrained by the gasstream although this is not usually preferred because of the greater gasrequirements and dust collection requirements of such a system.

The degree of fluidization can be readily controlled by varying thevelocity of the fluidizing gas or the intensity of mechanical agitation.

In the process of this invention, the composition and size of theproduct particles and ratio of core component material to partiallyhydrated salt in the particles can be readily controlled by varying theconcentration of core component material contained in the slurryintroducted, or varying the droplet size. For example, when introducinga slurry of a chlorinated isocyanurate salt containing 66% availablechlorine into a sodium tripolyphosphate bed, one can readily control theavailable chlorine content of the composite product particle by varyingthe concentration of chlorinated isocyanurate in the feed slurry. Suchfeed slurry containing 60% solids by weight will yield a final productassaying 16% chlorine while a feed slurry containing 33% solids yields afinal product at 6.5% available chlorine under comparable conditions.

The particle size of the composite product is closely related to theparticle size of the droplets of feed slurry impinging on the fluid bed,thus, a choice of nozzle characteristics and slurry pressure permitscontrol of the average particle size derived.

By controlling slurry droplet size and bed particle size as describedabove, a major portion of product particles desirably sized to pass a 10mesh and be retained on a 100 mesh US. Standard sieve are obtained.

It is seen that the process of this invention does not require aseparate drying step. This permits formation of products which areunique in terms of purity since thermal dehydration of inorganic saltssuch as sodium tripolyphosphate inherently results in degradation of asubstantial proportion of such salt to the pyrophosphate andorthophosphate forms may result in thermal degradation of the corecomponent material.

Particularly desirable products obtainable by the practice of thisinvention are compositions composed of particles comprising a corecomponent internally concentrated within a coating or matrix whichcomprises a major portion of partially hydrated phosphate salts at leas90% by dry weight of such salt being sodium tripolyphosphate. Suchparticles, wherein the core component is sodium hypochlorite, achlorocyanurate, an enzyme or other detergent ingredient areparticularly advantageous for use in cleaning and bleachingcompositions. If desired, various other materials can be incorporatedwith the hydrateable inorganic salt in the fluidized bed. For example, adye can be incorporated to provide a colored particle which may possesscertain esthetic appeal in a detergent formulation. Since the dye is, bythe practice of this process, peripherally concentrated, particles ofhigh color intensity are obtained with dye concentrations sufficientlylow that fabric discoloration problems are avoided.

The practice of this invention will be further understood from thefollowing examples.

EXAMPLE I 14,000 grams of particulate anhydrous phosphate salt assaying93 by weight sodium tripolyphosphate and having a mean particle size of25 microns are admixed with 14 grams finely dvided 1 micron) silica flowcondition and are introduced into a fiuidization apparatus having adiameter of 14 inches and fitted with a porous polyethylene grid at thebottom portion. The salt is vigorously fiuidizebd to about 1.4 timesstatic volume by passing air through the grid at about 60 cubic feet perminute.

An aqueous slurry containing 60% by weight sodium trichlorocyanurate(assaying 67% available chlorine on a dry basis) is sprayed onto the bedthrough a nozzle designed to provide a mean droplet diameter of about500 microns. 6820 grams of the slurry are introduced into the bed inabout 1.25 minutes. Bed temperature during the process increases from 30to 42 C.

A quantity of granular particles (smaller than 12 mesh, larger than 70mesh-US. Standard sieve sizes) equivalent to 58% by eight of feedmaterials to the bed is obtained.

Microscopic examination of particles broken and dampened with potassiumiodide solution to reveal the distribution of the chlorocyanurate, showsthe chlorocyanurate to be disposed predominantly at the center of theparticle. The composite particle contains about 65% phosphate salt.

Analysis shows the phosphate salt in the particles to be 93% sodiumtripolyphosphate demonstrating that no degradation takes place. The saltis 67% by weight hydrated-that is, the salt contains 67% as much wateras would be present in sodium tripolyphosphate hexahydrate.

Based on a comparison of chlorine loss, the particulate product is foundto be approximately 5 times as stable as a mere mixture comprising thesame initial concentrations of sodium tripolyphosphate and sodiumtrichlorocyanurate powder.

EXAMPLE II For purposes of comparison, the procedure of Example I isrepeated with the exception that a spray nozzle designed to provideslurry droplets not substantially larger than the salt particles in thefluidized bed is utilized.

In the product particles the chlorocyanurate is found to be randomlydistributed rather than preferentally concentrated. The particles aresignificantly less stable with regard to chlorine loss than thoseproduced by the procedure of Example 1.

EXAMPLE III For purposes of comparison, the procedure of Example I isrepeated utilizing sodium tripolyphosphate having a particle size ofabout 400 microns. In the product particles, chlorocyanurate is randomlydistributed and stability is significantly less than that of productparticles produced in Example I.

Example I above illustrates the practice of this invention. Example IIand III illustrating processes outside the scope of the inventiondemonstrate the criticality of the conditions specified for the practiceof this invention.

Although this invention has been described by reference to specificembodiments, various other embodiments within the scope of the appendedclaims will be apparent to those skilled in the art.

What is claimed is:

1. A method of making a composition composed of particles comprising acore component material selected from the group consisting of enzymesand chlorocyanurates and a partially hydrated inorganic salt selectedfrom the group consisting of Na P 01u, Na P O Na SO Na B O c1180. Na PONa CO N3-2HPO4 and partial hydrates thereof, said core componentmaterial being preferentially internally concentrated in said particle,said method comprising the steps of;

(a) forming a fluidized bed of particulate, hydrateable inorganic saltcomposed of a major proportion of particles from 5 microns to 200microns in size,

(b) introducing droplets of an aqueous slurry of said core componentmaterial into said fluidized bed, said droplets having a mean diameterfrom 10 to 30 times larger than the mean particle size of saidhydrateable inorganic salt, the amount of water introduced into thefluidized bed being less than stoichiometrically required for hydrationof said inorganic salt to the highest hydrate thereof.

2. The method of claim 1 herein said fluidized bed is pneumaticallyfluidized by a gas flow rate from 10% to 100% in excess of the minimumflow rate theoretically required to support said bed in a fluidizedstate.

3. The method of claim 1 wherein said hydrateable inorganic salt iscomposed of a major proportion of particles from 5 to 50 microns insize.

4. The method of claim 1 wherein said hydrateable inorganic salt issodium tripolyphosphate.

5. A method of making a composition composed of particles comprising achlorocyanurate and partially hydrated sodium tripolyphosphate, saidchlorocyanurate being preferentially internally concentrated in saidparticles, said method comprising the steps of (a) forming a fluidizedbed of particulate hydrateable sodium tripolyphosphate composed of amajor proportion of particles from 5 microns to 200 microns in size and(b) introducing droplets of an aqueous slurry of said chlorocyanurateinto said fluidized bed said droplets having a mean diameter from to 30times larger than the mean particle size of said sodiumtripolyphosphate, the amount of water introduced into the fluidized bedbeing less than stoichiometrically required for hydration of said sodiumtripolyphosphate to the highest hydrate thereof.

6. A method of making a composition composed of particles comprising anenzyme and partially hydrated sodium tripolyphosphate, said enzyme beingpreferentially internally concentrated in said particles, said methodcomprising the steps of (a) forming a fluidized bed of particulatehydrateable sodium tripolyphosphate composed of a major proportion ofparticles from 5 microns to 200 microns in size and (b) introducingdroplets of an aqueous slurry of said enzyme into said fluidized bed,said droplets having a mean diameter from 10 to times larger than themean particle size of said sodium tripolyphosphate, the amount of waterintroduced into the fluidized bed being less than stoichiometricallyrequired for hydration of said sodium tripolyphosphate to the highesthydrate thereof.

References Cited UNITED. STATES PATENTS 3,112,274 11/1963 Morgenthaleret a1. 25299 3,154,494 10/1964 Speak et a1; 25299 X 3,248,330 4/1966Feierstein et al. 25299 3,265,629 8/1966 Jensen 252316 3,354,090 11/1967Keast 25299 3,415,758 12/1968 Powell et al. 252316 RICHARD D. LOVERING,Primary Examiner US. Cl. X.R.

l17-l00 A, DIG 6; 25290, 95, 103,135, 156, 316, DIG 12

